1. Field of the Invention
This invention relates to a light emitting element made of a semiconductor material and a light emitting device using the light emitting element. Especially, this invention relates to a method of forming a low temperature-grown buffer layer that a Ga2O3 substrate does not deteriorate even when forming the low temperature-grown buffer layer in a H2 atmosphere, a method of making a light emitting element with GaN having an excellent crystalline quality by using the low temperature-grown buffer layer thus formed, the light emitting element, and a light emitting device using the light emitting element.
2. Description of the Related Art
GaN-based semiconductors are known as a material for light emitting element in blue or short-wavelength emission region. Especially, a light emitting element to emit ultraviolet light is estimated to be used for, e.g., a fluorescent lamp which is desired to be mercury-free in consideration of environment, a photocatalyst which provides a clean environment, a light source for a high-capacity recoding medium such as a DVD (digital versatile disk). The light emitting element is desired to have a further short-wavelength.
GaN is very high in melting point and in nitrogen equilibrium vapor pressure. Therefore, it is difficult to make a bulk single-crystal GaN substrate with a high quality and large area. Thus, a GaN growth method has been used that a sapphire (Al2O3) substrate is used as an underlying substrate, forming a buffer layer thereon to reduce the lattice mismatch with GaN, growing a GaN-based semiconductor thereon. However, a light emitting element using the GaN-based semiconductor has a limitation that its electrode structure is to be horizontally disposed. Further, it is desired that its lifetime and its handling easiness in mounting are further enhanced when it is applied to various uses.
Under these circumstances, it is recently proposed to use as a substrate β-Ga2O3, a transparent material, which is capable of transmitting ultraviolet light and of being manufactured as a bulk single crystal (See, e.g., Japanese Journal of Applied Physics., Vol. 44, No. 1, 2005 pp. L7-L8, hereinafter referred to as related art 1).
The related art 1 discloses a light emitting element that a low temperature-grown GaN buffer layer is formed on the β-Ga2O3 substrate at 600° C., and GaN is grown thereon at 1070° C.
However, the light emitting element of the related art 1 has a problem that β-Ga2O3 may be thermally decomposed in the process of forming the low temperature-grown GaN buffer layer and therefore it is difficult to grow a high-quality GaN-based semiconductor layer thereon in a subsequent process.
It is generally known that the GaN buffer layer is formed on the β-Ga2O3 substrate in a H2 atmosphere. It is exactly found by the inventors that the surface of the β-Ga2O3 substrate deteriorates into black when the buffer layer is formed at a temperature higher than 600° C. in the H2 atmosphere.